The present invention relates to an intake system or device of an outboard motor mounted with a V-type engine unit.
There is known a technology concerning an intake system of a four-stroke-cycle reciprocal engine in which length of an intake passage connecting a surge tank and an intake port is constructed to be variable into two stages to thereby enhance an intake air filling efficiency along a wide revolution area of the engine, as disclosed, for example, in Japanese Patent Laid-open Publication No. HEI 7-102979. In this known publication, there are arranged, above the V-type engine, an intake passage for high revolution (speed) area and an intake passage for intermediate and low revolution area along a lower surface of a surge tank having a flat shape expanding in the width direction of the engine, and the intake passage for the intermediate and low revolution area has substantially a linear shape extending in the width direction of the V-type engine.
However, according to the arrangement of the known art mentioned above, since the surge tank has a flat shape expanding in the engine width direction above the engine, the surge tank occupies a large space above the V-type engine. Furthermore, in a case where such layout is applied to an outboard motor mounted with a vertical type engine, the surge tank is located on the rear side of the engine and an engine cover having a large size or dimension is therefore required, which results in enlargement of the rear portion of the outboard motor body in the width direction thereof.
A boat or like equipped with the outboard motor changes its advancing direction by rotating (pivoting) the outboard motor with respect to a hull (stern) of the boat, and accordingly, it is not desirable to widen the width of the rear portion of the outboard motor for the reason that the rotating angle, i.e. steering angle, of the outboard motor is reduced. Moreover, In a case of an arrangement of two outboard motors at the rear portion of the hull, there is a fear of interference of these outboard motors from each other at the time of steering operation of large angles.
In order to reduce the width of the rear portion of the outboard motor, it may be considered to reduce an inner volume of the surge tank. However, such countermeasure is not desirable in terms of intake performance.
Furthermore, the above prior art provides a structure in which an intake passage for a low/intermediate revolution operation of the engine is formed linearly so as to provide a short length of about xc2xd (half) of the width of a surge tank, which provided inconvenience in the intake filling coefficiency at the low/intermediate revolution area of the engine.
Still furthermore, because of the structure in which the surge tank has a flat shape and a wall portion thereof is disposed in the vicinity of an inlet of the intake passage for high revolution operation, there also provided inconvenience in the intake filling coefficiency at the high revolution area of the engine.
An object of the present invention is to substantially eliminate defects or inconveniences encountered in the prior art mentioned above and to provide an intake system of an outboard motor having a structure capable of improving an engine performance around substantially all the engine revolution operation area, making compact an entire structure of the outboard motor, ensuring a large steering angle of a hull and easily manufacturing the outboard motor at a reduced cost.
This and other objects can be achieved according to the present invention by providing an intake system of an outboard motor, which includes a vertically arranged V-type engine having a crankshaft extending perpendicularly therein and right and left cylinder banks opened in V-shape towards a rear side as viewed in a plan view, and in which intake ports of respective cylinders are opened to the inside of the V-shape arrangement, the intake system comprising:
an intake manifold connected to the intake ports;
a surge tank connected to the intake manifold and disposed at a rear side from a central portion of the engine;
a throttle body mounted to the surge tank and provided with a throttle valve;
a plurality of intake passages for high revolution operation of the engine, the intake passages for high revolution operation extending from the surge tank and being communicated with the intake manifold, the plural intake passages for high revolution operation having a number corresponding to a number of the cylinders of the engine;
a plurality of intake passages for low/intermediate revolution operation of the engine, the intake passages for low/intermediate revolution operation extending from the surge tank and being joined with the intake passages for high revolution operation, respectively, the plural intake passages for low/intermediate revolution operation having a number corresponding to a number of the cylinders of the engine and each of the intake passages for low/intermediate revolution operation having a length longer than that for high revolution operation; and
a valve open/close mechanism disposed for opening/closing all at once portions upstream side of the joined portions of the intake passages for low/intermediate revolution operation and those for high revolution operation,
the intake passages for low/intermediate revolution operation extending, as viewed in a plan view, from both side surfaces of the surge tank towards both outsides in a width direction of an outboard motor body so as to be positioned at a rear portion of both the cylinder banks of the V-type engine, so that the surge tank and the intake passages for low/intermediate revolution operation provides a protrusion protruding towards a rear side of the engine.
According to the structure of the intake system of the outboard motor of the present invention, the air in the surge tank flows towards the intake ports, when the valve open/close mechanism is closed, through the intake passages for low/intermediate revolution operation of the engine each having a long length in comparison with that of the intake passage for high revolution operation, and on the contrary, flows towards the intake ports, when the valve open/close mechanism is opened, through the the intake passages for high revolution operation of the engine each having a short length in comparison with that of the intake passage for low/intermediate revolution operation. Accordingly, by controlling the valve open/close mechanism so as to be closed at the time of the engine low revolution operation and, on the contrary, to be opened at the time of the engine high revolution operation, the intake passages suitable for the respective engine revolution areas are obtainable, and moreover, the intake filling efficiency can be ensured at the wide engine revolution operation area, thus improving the engine performance.
Furthermore, the surge tank and the intake passages for low/intermediate revolution operation are formed to have a protrusion protruding towards a rear side of the engine. According to this structure, the expansion of the surge tank in the width direction of the outboard motor body can be prevented without reducing the volume of the surge tank, so that the outboard motor body can be made compact, and the large steering angle of the hull can be also ensured.
In preferred embodiment of the above aspect of the present invention, the plural intake passages for low/intermediate revolution operation includes a half for left-side cylinder bank of the V-type engine to a right side of the surge tank and another half for right-side cylinder bank of the V-type engine to a left side of the surge tank so that axial directions of the intake passages for low/intermediate revolution operation at the joining portions thereof to the intake passages for high revolution operation substantially accord with axial directions of the passages of the intake manifold.
Each of the intake passages for low/intermediate revolution operation once extends towards both outside directions from a width direction of the outboard motor body, is turned in U-shape in a vertical direction and then extends again towards an inside in the width direction of the outboard motor body to thereby join the intake passages for low/intermediate revolution operation to the intake passages for high revolution operation.
The intake passages for high revolution operation of the engine is provided with surge thank side inlets arranged in a vertical single line in parallel to the crankshaft of the engine, the valve open/close mechanism includes a plurality of butterfly valves disposed at the surge tank side inlets, and the butterfly valves are provided with a single valve rotating shaft having an axis substantially in parallel to the crankshaft of the engine.
The valve open/close mechanism includes a plurality of butterfly valves disposed at surge tank side inlets of the intake passages for high revolution operation, an actuator, as driving means, mounted to a lower end of the valve rotating shaft extending from the lower surface of the surge tank, and an expansion rod extending from the actuator to be connected to the crankshaft connected to the valve rotating shaft. Moreover, the throttle valve is provided for vertical one end of the surge tank and the valve open/close mechanism includes a drive member provided for another one end of the surge tank.
The V-type engine is a water-cooled 6-cylinder V-type engine, three in each side of V-arrangement.
The surge tank is provided with a lid member.
The surge tank, the intake passages for high revolution operation of an engine and the intake passages for low/intermediate revolution operation of the engine are divided into front and rear halves from a division surface along an extending direction of the intake passages for low/intermediate revolution operation.
According to such preferred embodiment, in the case where the intake passage for low/intermediate revolution operation of the engine becomes long, the passage from the intake passage for low/intermediate revolution operation to the portion connected to the intake manifold becomes substantially linear, thus reducing the intake resistance, and hence, the engine operation performance in the low/intermediate revolution area of the engine can be improved.
Still furthermore, the butterfly valves of the valve open/close mechanism can be driven by a single valve rotating shaft disposed in parallel to the engine crankshaft. Therefore, the structure of the intake system can be made compact and easily manufactured, thus improving maneuverability and reliability in performance and reducing occurrence of defect.
Still furthermore, the improved arrangement of the surge tank makes possible to effectively use the inner space of the engine cover and the inner volume of the surge tank can be made large.
The natures and further characteristic features of the present invention can be mode more clear from the following descriptions made with reference to the accompanying drawings.